Can a macro bellows reduce focus breathing for focus stacking?
Asked 4/26/2020
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I want to automate focus stacking with a manual macro lens while minimizing focus breathing (changes in framing/magnification as focus changes). Would a motorized macro bellows help if it changes the lens extension while the camera stays still? If not, what setup minimizes breathing the most? Could moving the camera in relation to the lens compensate for framing changes?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
6y ago
2 Answers
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A bellows that moves the camera body while keeping the lens (and subject) stationary is the best option. By moving the camera body you shift the sensor through the DOFocus at the image plane, which keeps the lens' perspective constant. This should result in the minimum of image shifts assuming the stack isn't really deep... but such a setup is uncommon.
However, all methods of shifting the focus result in some image/magnification shift. If you use a bellows it introduces the bellows factor which changes the relative size of the image circle, which changes the light density/exposure, and the apparent magnification. If you shift the lens/camera together it changes the perspective which changes the relative distances/sizes. And if you shift the focus (ring) it changes the magnification.
Originally by user70370. Source · Licensed CC BY-SA 4.0
user70370
6y ago
0
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A bellows can help, but it does not completely eliminate framing or magnification changes.
From the approaches mentioned, the best option is a setup that moves the camera body while keeping the lens and subject stationary. That shifts the sensor through the plane of focus at the image plane, so the lens perspective stays constant and image shift is minimized.
If instead the bellows changes lens extension with the camera fixed, magnification still changes, so you will still see some breathing/framing change. Turning the focus ring also changes magnification. Moving the whole camera/lens assembly changes perspective, which also alters relative sizes and framing.
So the key point is: all focus-stacking methods introduce some shift. The least-breathing option is moving the camera body relative to a fixed lens/subject, though this is an uncommon setup. Bellows extension also changes effective exposure (bellows factor), so exposure may need adjustment across the stack.
In practice, expect some residual size shift and plan to align frames in stacking software.
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